In the state of the art of capacitive sensor devices, capacitive conditions between a sensor surface and an object present in the detecting range of the sensor device are measured or detected. The object present in the detecting range distorts the alternating electrical field in the detecting range. The measurement results allow conclusions to be drawn about the distance between the measurement electrodes of the sensor surface and the object and/or the position of the object relative to the sensor surface. The relationship between the object distance or position of the object and the measurement results is strongly non-linear.
If more than one object is present in the detecting range of the sensor device, then each individual object affects the distortion of the single alternating electrical field. The relationship between the measured values or measurement results and the distances of the objects from the sensor surface or the positions of the objects relative to the sensor surface becomes more complex as the number of objects increases, because the sensor measurement values no longer depend only on the position or distance of a single object. Precise detection of the distances of a plurality of objects from the sensor surface or the positions of a plurality of objects relative to the sensor surface can thereby no longer be guaranteed.
If the independence of some sensor measurement values from the distance or position of certain objects is nevertheless assumed for estimating the distance or position, this leads to systematic measurement errors that can cause artifacts. In the worst case, the measurement errors can lead to the distance or position of the object no longer being able to be detected or estimated.
In a concrete application for two-handed operation of a device having a capacitive sensor device, it is desirable to detect the positions of both hands or a plurality of fingers relative to the sensor device independently of each other.
Due to the sensitivity of the sensor measurement values, which depend on the distance of the objects from the sensor surface, the disturbance of the measurement value for a first nearby object due to field distortion caused by a second, more distant object is relatively small, so that the distance or position of the first object can be detected reliably. Conversely, the distance or position of the second object cannot be reliably detected, however.
In the prior art, attempts are being made to solve this problem by a large number of sensor electrodes being provided at the sensor surface, disposed at a short distance from each other. Individual sensor electrodes or a plurality of adjacent sensor electrodes can then be used for determining the distance or position of an object, albeit under the assumption that the influence of other objects on the measurement values of said electrodes is negligible. A further prerequisite for this approach, however, is that the distance of the objects from each other does not fall below a predetermined value. This applies particularly to greater distances of the objects from the sensor surface, i.e. if the sensor electrodes are less sensitive, and for distances between sensor electrodes that are small relative to the distance of the object from the sensor surface, thereby producing unfavorable geometric conditions for determining the X-Y position.
A further solution approach known from the prior art consists of spatially separating a plurality of sensor device or sensor electrodes from each other, so that each sensor device or sensor electrode forms or defines its own detecting range. Measurement values of a sensor device are thus associated with a corresponding object, while measurement values of a different sensor device are associated with the other object. In order to determine the distance or position of an object, sensor electrodes of a single sensor device can then be used or considered exclusively, wherein here again the assumption must be made that the influence of each of the other objects on the measurement values of said sensor device is negligible.
This solution approach is only practical, however, if there is sufficient spatial separation of the sensor devices or sensor electrodes.